Vertically free standing nanostructures, because of their large surface area and their adaptability to different surface chemistries, are increasingly being used to improve the performance of bioimpedance and biopotential based medical devices, solar energy conversion, thermoelectric devices, super capacitors, quantum wires, optoelectronic devices, fuel cells, and lithium-ion based batteries.
The fabrication process of nanosensors, such as roll to roll printing, screen printing, cleanroom thin-film fabrication technology, template assisted growth of vertically standing nanostructures, require quality checks for consistent results. Measurement of nanoparticles/nanostructures that are part of the surface, nanocomposite or coatings of the nanosensor is important for application specific nanosensor properties.
Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) techniques are the main tools of nanoparticles/nanostructure metrology. The measurement involves analysis of many representative samples of the nanosensor product, taken from the process line, in order to ensure consistency of nanosensor properties. But the current AFM and SEM techniques lack automation and limitations in the known AFM techniques in scanning vertical structures with high aspect ratio prevents them from being used for fast and accurate analysis of vertically free standing nanostructures which are made of materials with different moduli of elasticity, e.g., from rigid metals and metal oxides to soft polymers.
Complete nanoparticle/nanostructure measurement and analysis involve size distribution measurements (using SEM), interior structure measurements (using Tunneling Electron Microscopy), elemental analysis (using SEM-Energy Dispersive X-ray spectroscopy), surface roughness measurements (using AFM), nanostructure dimension measurements (using AFM), mechanical strength measurements (using AFM), as well as electrical, electromagnetic, and chemical property analysis (using AFM). Conventional AFM and SEM face challenges especially in case of free standing nanostructures. The free standing nanostructures with high aspect ratio, which may be rigid or flexible, are difficult to scan at the tip because they are susceptible to movement/vibration and may have different tilt, i.e. not all of the tips face up with 0° incline/tilt.
With few exceptions such as Atomic Force Scanning Electron Microscopy Systems (AFSEMS) from Semilabsinc. and Agar Scientific, SEM and AFM are done separately. Since they are done separately, there is no way to collate SEM and AFM of the same nanostructures over a large number of nanostructures on a surface.
Atomic Force Scanning Electron Microscopy Systems (AFSEMS) have an AFM stage mounted within the SEM chamber to enable simultaneous scanning. However, while this provides an AFM combined with SEM, it still does not solve limitation of AFM in case of scanning vertical structures with high aspect ratio and it limits AFM applications to dry sample scanning only. Wet SEM technology such as QuantomiX WETSEM, uses a capsule to keep the wet sample within, thus not allowing for an AFM probe to reach the sample. Further, the SEM chamber limits the AFM in measurement of conductivity, electromagnetic testing of the nanostructure and limits AFM methods to study mechanical properties of nanostructures. Performing SEM and AFM separately on large number of samples is a cumbersome task and is prone to errors because of the manual processes involved in moving and preparing the samples.